U.S. patent application number 11/029628 was filed with the patent office on 2005-07-14 for adhesive film for circuit connection, and circuit connection structure.
Invention is credited to Fukushima, Naoki, Kume, Masahide, Tatsuzawa, Takashi, Watanabe, Itsuo.
Application Number | 20050151271 11/029628 |
Document ID | / |
Family ID | 34737115 |
Filed Date | 2005-07-14 |
United States Patent
Application |
20050151271 |
Kind Code |
A1 |
Tatsuzawa, Takashi ; et
al. |
July 14, 2005 |
Adhesive film for circuit connection, and circuit connection
structure
Abstract
The present invention provides an adhesive film for circuit
connection which is to be interposed between circuit electrodes
facing each other and used for electrically connecting the circuit
electrodes to each other, which comprises a curing agent to
generate free radicals with heating, a radically polymerizable
substance, and a film-forming polymer, and in which a temporary
fixing power to a flexible substrate having the circuit electrode
is 40-180 N/m.
Inventors: |
Tatsuzawa, Takashi;
(Shimodate-shi, JP) ; Watanabe, Itsuo;
(Shimodate-shi, JP) ; Fukushima, Naoki;
(Shimodate-shi, JP) ; Kume, Masahide;
(Shimodate-shi, JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW
SUITE 700
WASHINGTON
DC
20036
US
|
Family ID: |
34737115 |
Appl. No.: |
11/029628 |
Filed: |
January 6, 2005 |
Current U.S.
Class: |
257/783 ;
257/E21.514; 257/E23.018; 428/209 |
Current CPC
Class: |
H01L 2924/09701
20130101; H01L 2924/014 20130101; Y10T 428/2857 20150115; C09J 7/10
20180101; H01L 2224/838 20130101; H01L 2924/01082 20130101; H01L
2224/83101 20130101; H01L 24/29 20130101; H01L 2924/0781 20130101;
C09J 2433/00 20130101; H01L 2924/01013 20130101; H01L 2924/01015
20130101; H01L 2924/0105 20130101; H01L 2224/05568 20130101; H01L
2224/05573 20130101; H01L 23/4828 20130101; H01L 2924/01033
20130101; H01L 2924/01045 20130101; H01L 2924/01047 20130101; H01L
2924/01027 20130101; H01L 2924/01029 20130101; Y10T 428/2896
20150115; H01L 2224/2919 20130101; H01L 2924/0665 20130101; H01L
24/83 20130101; H01L 24/16 20130101; H01L 2224/16 20130101; H01L
2924/01005 20130101; H01L 2924/01006 20130101; H01L 2924/07811
20130101; Y10T 428/24917 20150115; H01L 2924/01074 20130101; H01L
2924/01078 20130101; H01L 2924/01079 20130101; H05K 3/323 20130101;
H01L 2224/2919 20130101; H01L 2924/0665 20130101; H01L 2924/00
20130101; H01L 2924/0665 20130101; H01L 2924/00 20130101; H01L
2924/07811 20130101; H01L 2924/00 20130101 |
Class at
Publication: |
257/783 ;
428/209 |
International
Class: |
H01L 023/48; B32B
003/00; H04L 012/28 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 7, 2004 |
JP |
P2004-002326 |
Claims
What is claimed is:
1. An adhesive film for circuit connection, which is to be
interposed between circuit electrodes facing each other and used
for electrically connecting the circuit electrodes to each other,
the adhesive film comprising: a curing agent to generate free
radicals with heating; a radically polymerizable substance; and a
film-forming polymer, wherein a temporary fixing power to a
flexible substrate having the circuit electrode is 40-180 N/m.
2. The adhesive film for circuit connection according to claim 1,
wherein the radically polymerizable substance is a radically
polymerizable substance having a viscosity at 25.degree. C. in a
range of 100,000 mpa.s to 1,000,000 mPa.s.
3. The adhesive film for circuit connection according to claim 2,
wherein the curing agent is an organic peroxide whose temperature
for the half-life of 10 hours is not less than 40.degree. C. and
whose temperature for the half-life of 1 minute is not more than
180.degree. C.
4. The adhesive film for circuit connection according to claim 3,
wherein an amount of the organic peroxide formulated is 0.05-10% by
weight.
5. The adhesive film for circuit connection according to claim 2,
wherein the radically polymerizable substance has a tricyclodecanyl
group.
6. The adhesive film for circuit connection according to claim 5,
wherein the radically polymerizable substance is an acrylate or a
methacrylate.
7. The adhesive film for circuit connection according to claim 2,
wherein the radically polymerizable substance comprises an urethane
acrylate or an urethane methacrylate.
8. The adhesive film for circuit connection according to claim 2,
wherein the radically polymerizable substance comprises a radically
polymerizable substance having a triazine ring.
9. The adhesive film for circuit connection according to claim 2,
wherein the film-forming polymer is contained in an amount of
80-180 parts by weight, relative to 100 parts by weight of the
radically polymerizable substance.
10. The adhesive film for circuit connection according to claim 2,
wherein a molecular weight of the film-forming polymer is
10,000-1,000,000.
11. The adhesive film for circuit connection according to claim 2,
further comprising electrically conductive particles.
12. The adhesive film for circuit connection according to claim 11,
wherein the electrically conductive particles have a coating layer
of a noble metal on a transition metal and wherein a thickness of
the coating layer is not less than 30 nm.
13. The adhesive film for circuit connection according to claim 2,
further comprising a filler within a range of 5 to 60% by
volume.
14. The adhesive film for circuit connection according to claim 11,
comprising a first layer containing the curing agent, and a second
layer containing the electrically conductive particles.
15. A circuit connection structure obtained in the following
manner: at least one of a first circuit member having a first
circuit electrode and a second circuit member having a second
circuit electrode is a flexible substrate; the adhesive film for
circuit connection as defined in claim 1 or 2 is temporarily fixed
to the flexible substrate; the first circuit member and the second
circuit member are placed in a state in which the first circuit
electrode and the second circuit electrode face each other; the
adhesive film for circuit connection is interposed between the
first circuit electrode and the second circuit electrode placed in
the facing state; the adhesive film for circuit connection is
heated and pressed to electrically connect the first circuit
electrode and the second circuit electrode to each other.
16. A circuit connection structure comprising: a first circuit
member in which a first circuit electrode is formed on a first
circuit substrate; a second circuit member in which a second
circuit electrode is formed on a second circuit substrate; and a
circuit connection member placed between the first circuit
electrode and the second circuit electrode and connecting the first
and second circuit members to each other, wherein the circuit
connection member is a cured product of the adhesive film for
circuit connection as defined in claim 1 or 2 and wherein the first
circuit electrode and the second circuit electrode are electrically
connected through the circuit connection member.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an adhesive film for
circuit connection, and a circuit connection structure.
[0003] 2. Related Background Art
[0004] Circuit-connection films for electrically connecting
mutually opposed circuit electrodes, e.g., anisotropic conductive
adhesive films in which electrically conductive particles are
dispersed in an epoxy type adhesive (epoxy resin base anisotropic
conductive adhesive films) are commonly used for electrical
connection mainly between a TCP (Tape Carrier Package) equipped
with a semiconductor chip for driving a liquid crystal display
(LCD; Liquid Crystal Display), and an LCD panel, or between a TCP
and a printed circuit board.
[0005] In recent years, even in cases where a semiconductor chip is
mounted directly on an LCD panel or on a printed circuit board by
face down bonding, the flip chip packaging advantageous for
thickness reduction and narrow pitch connection is adopted instead
of the conventional wire bonding method, and the anisotropic
conductive adhesive films are also used as circuit-connection
adhesive films in this packaging.
[0006] However, the aforementioned epoxy resin base anisotropic
conductive adhesive films had excellent workability but required
heating at about 160-180.degree. C. for the connection time of
about 20 seconds and heating at about 180-210.degree. C. for 10
seconds.
[0007] The reason for the need for such heating is that a catalyst
curing agent inactive at ordinary temperature is used for the
purpose of achieving good stability through simultaneous
achievement of short-time curability (fast curability) and storage
stability (shelf life) and it results in failing to achieve
sufficient reaction during curing.
[0008] With recent trends toward larger scale and narrower frame of
LCD modules, there arise problems of increase of thermal influence
on the LCD panel and increase of warpage of the printed board in a
connection operation with use of the circuit-connection adhesive
film. There are also studies on replacement of the glass LCD panel
substrate with a plastic one in terms of weight reduction, but the
plastic materials have the problem of low thermal resistance to
make mounting of the TCP difficult.
[0009] There are thus demands for low-temperature connection of the
circuit-connection adhesive film as countermeasures to such
problems. In addition, low-temperature fast curability is necessary
and indispensable in order to meet needs for reduction of the
connection time to below 10 seconds to increase production
efficiency. For this reason, there are proposals of
circuit-connection adhesive films with a radically polymerizable
substance capable of achieving connection by heating at about
160.degree. C. for the connection time of 10 seconds (e.g.,
Japanese Patent No. 3344886).
SUMMARY OF THE INVENTION
[0010] The Inventors found that the foregoing circuit-connection
adhesive films with the radically polymerizable substance had the
problem of poor connection processability; for example, in a
pre-bonding process of transferring the circuit-connection adhesive
film onto circuit electrodes of a substrate, the film failed to be
accurately transferred onto the circuit electrodes of the
substrate; or, after a process of temporarily fixing a circuit
member to be connected, to the circuit-connection adhesive film,
the circuit member peels off the circuit-connection adhesive film
because of vibration during transportation to a main bonding
process.
[0011] An object of the present invention is to provide an adhesive
film for circuit connection and a circuit connection structure with
excellent connection processability during connection between
circuit members.
[0012] In order to achieve the above object, the present invention
provides an adhesive film for circuit connection, which is to be
interposed between circuit electrodes facing each other and used
for electrically connecting the circuit electrodes to each other,
the adhesive film comprising a curing agent to generate free
radicals with heating, a radically polymerizable substance, and a
film-forming polymer, wherein a temporary fixing power to a
flexible substrate having the circuit electrode is 40-180 N/m.
[0013] This adhesive film for circuit connection has excellent
connection processability in connecting circuit electrodes of
circuit members to each other. Specifically, an improvement is made
in transferability onto a flexible substrate as a circuit member.
In addition, a flexible substrate as a circuit member becomes
unlikely to drop with vibration during transportation to a next
process. Furthermore, after a process of transferring the adhesive
film for circuit connection onto a flexible substrate, the
circuit-connection adhesive film becomes unlikely to peel off a
base film (also called a strippable support film) normally used as
bonded to the circuit-connection adhesive film. Yet furthermore,
even if the circuit-connection adhesive film several ten meters or
more long is wound around a reel and kept still at room temperature
for a long time, back transfer of the circuit-connection adhesive
film onto the base film is adequately prevented. Thus it well
overcomes the problem that the circuit-connection adhesive film
cannot be drawn out of the reel.
[0014] If the temporary fixing power is lower than 40 N/m,
tackiness will be too weak; after a process of temporarily fixing a
flexible substrate to the circuit-connection adhesive film, the
flexible substrate becomes likely to drop with vibration during the
transportation to the next process, thus degrading the connection
processability, or productivity. On the other hand, if the
temporary fixing power of the adhesive film is larger than 180 N/m,
tackiness will be too strong; after a process of transferring the
adhesive film onto a flexible substrate, the adhesive film will
hardly peel off the base film, similarly causing a problem of
reduction of productivity. In addition, the too strong tackiness
will cause a problem that, where the circuit-connection adhesive
film several ten meters or more long is wound around a reel and
kept still at room temperature for a long time, the
circuit-connection adhesive film is back-transferred onto the base
film and the desired circuit-connection adhesive film cannot be
drawn out of the reel.
[0015] A circuit connection structure of the present invention is
obtained as follows: at least one of a first circuit member having
a first circuit electrode and a second circuit member having a
second circuit electrode is a flexible substrate; the
aforementioned adhesive film for circuit connection is temporarily
fixed to the flexible substrate; the first circuit member and the
second circuit member are placed in a state in which the first
circuit electrode and the second circuit electrode face each other;
the circuit-connection adhesive film is interposed between the
first circuit electrode and the second circuit electrode placed in
the facing state; the circuit-connection adhesive film is heated
and pressed to electrically connect the first circuit electrode and
the second circuit electrode to each other.
[0016] The present invention also provides a circuit connection
structure comprising a first circuit member in which a first
circuit electrode is formed on a first circuit substrate; a second
circuit member in which a second circuit electrode is formed on a
second circuit substrate; and a circuit connection member placed
between the first circuit electrode and the second circuit
electrode and connecting the first and second circuit members to
each other, wherein the circuit connection member is comprised of a
cured product of the aforementioned adhesive film for circuit
connection and wherein the first circuit electrode and the second
circuit electrode are electrically connected through the circuit
connection member.
[0017] In these circuit connection structures, the adhesive film
provides excellent connection processability in connecting the
circuit members to each other. For this reason, it becomes feasible
to increase productivity and to reduce the cost of the circuit
connection structure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a sectional view showing an embodiment of the
circuit connection structure according to the present
invention.
[0019] FIG. 2 is a step diagram showing a series of production
steps of the circuit connection structure of FIG. 1.
[0020] FIG. 3 is a sectional view schematically showing an
embodiment of the adhesive film for circuit connection according to
the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] An adhesive film for circuit connection according to the
present invention will be described below.
[0022] The adhesive film for circuit connection according to the
present invention is a circuit-connection adhesive film which is to
be interposed between circuit electrodes facing each other and used
for electrically connecting the circuit electrodes to each other,
the adhesive film comprising a curing agent to generate free
radicals with heating, a radically polymerizable substance, and a
film-forming polymer, wherein a temporary fixing power to a
flexible substrate having the circuit electrode is 40-180 N/m.
[0023] This circuit-connection adhesive film has excellent
connection processability to a flexible substrate being a circuit
member. Specifically, an improvement is made in transferability to
the flexible substrate with circuit electrodes. In addition, the
flexible substrate becomes unlikely to drop with vibration during
transportation to the next process. Furthermore, after the process
of transferring the circuit-connection adhesive film onto the
flexible substrate, the circuit-connection adhesive film becomes
unlikely to peel off the base film. Yet furthermore, even in the
case where the circuit-connection adhesive film several ten meters
or more long is wound around a reel and kept still at room
temperature for a long time, the back transfer of the
circuit-connection adhesive film onto the base film is adequately
prevented to well overcome the problem that the desired
circuit-connection adhesive film cannot be drawn out of the
reel.
[0024] If the temporary fixing power is lower than 40 N/m,
tackiness will be too weak; after a process of temporarily fixing a
flexible substrate to the circuit-connection adhesive film, the
flexible substrate becomes likely to drop with vibration during the
transportation to the next process, thus degrading the connection
processability, or productivity. On the other hand, if the
temporary fixing power of the adhesive film is larger than 180 N/m,
tackiness will be too strong; after a process of transferring the
adhesive film onto a flexible substrate, the adhesive film will
hardly peel off the base film, similarly causing a problem of
reduction of productivity. In addition, the too strong adherence
will likely cause a problem that, where the circuit-connection
adhesive film several ten meters or more long is wound around a
reel and kept still at room temperature for a long time, the
circuit-connection adhesive film is back-transferred onto the base
film and the desired circuit-connection adhesive film cannot be
drawn out of the reel.
[0025] A sample for measuring the temporary fixing power of the
circuit-connection adhesive film of the present invention is
prepared as follows. Namely, a circuit-connection adhesive film
with a PET base 2.5 mm wide is first pre-bonded under the
conditions of 70.degree. C., 1 MPa, and 3 s onto an ITO-coated
glass (surface resistance: 15-20 .OMEGA./.quadrature.; thickness:
1.1 mm) substrate; thereafter the PET base is peeled off; a 200
.mu.m pitch flexible circuit board (18 .mu.m Cu foil, plated with
Sn) with the base of a 75 .mu.m-thick polyimide film is bonded
under the conditions of 20-24.degree. C., 0.5 MPa, and 5 s onto the
circuit-connection adhesive film to prepare the sample for
temporary fixing.
[0026] The measurement of the temporary fixing power is carried out
as follows. Namely, using the sample prepared as described above, a
bond strength (per cm in width) between the 200 .mu.m pitch
flexible printed circuit board (FPC) and the circuit-connection
adhesive film is measured (at the measurement temperature of
23.+-.2.degree. C.) by peeling in the tensile direction of
90.degree. (at the tensile speed: 50 mm/min) (peeling in the
parallel direction to circuits of FPC), and the bond strength
measured at this time is defined as a temporary fixing power
(N/m).
[0027] A particularly preferred range of the temporary fixing power
of the circuit-connection adhesive film according to the present
invention is 60 N/m-150 N/m.
[0028] The curing agent to generate free radicals with heating,
which is applicable in the present invention, is an agent that is
decomposed with heating to generate free radicals, and there are no
particular restrictions on the curing agent as long as it, together
with the radically polymerizable substance and the film-forming
polymer, can achieve the temporary fixing power of 40-180 N/m of
the circuit-connection adhesive film to the flexible substrate.
Examples of the curing agent include curing agents such as
peroxides and azo compounds The curing agent is properly selected
according to a target connection temperature, a target connection
time, a target pot life, and so on. Among the aforementioned
peroxides, in terms of high reactivity and pot life, it is
preferable to use an organic peroxide whose temperature for the
half-life of ten hours is not less than 40.degree. C. and whose
temperature for the half-life of one minute is not more than
180.degree. C. In this case, a content of the organic peroxide
mixed is preferably 0.05-10% by weight and more preferably 0.1-5%
by weight. If the content of the organic peroxide is less than
0.05% by weight, the organic peroxide becomes less reactive, when
compared with the case where the content is not less than 0.05% by
weight. On the other hand, if the content of the organic peroxide
exceeds 10% by weight, the stability of preservation becomes lower,
when compared with the case where the content is not more than 10%
by weight. Specifically, the curing agent can be selected from
diacyl peroxides, peroxydicarbonates, peroxyesters, peroxyketals,
dialkylperoxides, hydroperoxides, and so on. In order to suppress
corrosion of circuit electrodes of circuit members, the curing
agent is preferably selected from peroxyesters, dialkylperoxides,
and hydroperoxides, and is more preferably selected from
peroxyesters to provide high reactivity.
[0029] Examples of the diacyl peroxides include isobutyl peroxide,
2,4-dichlorobenzoyl peroxide, 3,5,5-trimethylhexanoyl peroxide,
octanoyl peroxide, lauroyl peroxide, stearoyl peroxide, succinic
peroxide, benzoyl peroxytoluene, benzoyl peroxide, and so on.
[0030] Examples of the peroxydicarbonates include di-n-propyl
peroxydicarbonate, diisopropyl peroxydicarbonate,
bis(4-t-butylcyclohexyl- )peroxydicarbonate,
di-2-ethoxymethoxyperoxydicarbonate,
di(2-ethylhexylperoxy)dicarbonate, dimethoxybutyl
peroxydicarbonate, di(3-methyl-3-methoxybutylperoxy)dicarbonate,
and so on.
[0031] Examples of the peroxyesters include cumyl
peroxyneodecanoate, 1,1,3,3-tetramethylbutyl peroxyneodecanoate,
1-cyclohexyl-1-methylethyl peroxynoedecanoate, t-hexyl
peroxyneodecanoate, t-butyl peroxypivarate,
1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate,
2,5-dimethyl-2,5-bis(2-- ethylhexanoylperoxy)hexane,
1-cyclohexyl-1-methylethyl peroxy-2-ethylhexanoate, t-hexyl
peroxy-2-ethylhexanoate, t-butyl peroxy-2-ethylhexanoate, t-butyl
peroxyisobutyrate, 1,1-bis(t-butylperoxy)cyclohexane, t-hexyl
peroxyisopropylmonocarbonate, t-butyl
peroxy-3,5,5-trimethylhexanoate, t-butyl peroxylaurate,
2,5-dimethyl-2,5-bis(m-toluoylperoxy)hexane, t-butyl
peroxyisopropylmonocarbonate, t-butyl
peroxy-2-ethylhexylmonocarbonate, t-hexyl peroxybenzoate, t-butyl
peroxyacetate, and so on.
[0032] Examples of the peroxyketals include
1,1-bis(t-hexylperoxy)-3,3,5-t- rimethylcyclohexane,
1,1-bis(t-hexylperoxy)cyclohexane,
1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,
1,1-(t-butylperoxy)cyclododecane, 2,2-bis(t-butylperoxy)decane, and
so on.
[0033] Examples of the dialkyl peroxides include .alpha.,
.alpha.'-bis(t-butylperoxy)diisopropylbenzene, dicumyl peroxide,
2,5-dimethyl-2,5-di(t-butylperoxy)hexane, t-butylcumyl peroxide,
and so on.
[0034] Examples of the hydroperoxides include diisopropylbenzene
hydroperoxide, cumene hydroperoxide, and so on. These free radical
generators may be used alone or in combination and may also be used
as mixed with a decomposition accelerator or inhibitor, or the
like.
[0035] The radically polymerizable substance used in the present
invention is a substance having a functional group capable of
undergoing radical polymerization, and the radically polymerizable
substance can be selected from acrylates, methacrylates, maleimide
compounds, and so on.
[0036] Specific examples of the acrylates (methacrylates) include
urethane acrylate, methyl acrylate, ethyl acrylate, isopropyl
acrylate, isobutyl acrylate, ethylene glycol diacrylate, diethylene
glycol diacrylate, triethylene glycol diacrylate,
trimethylolpropane triacrylate, tetramethylolmethane tetraacrylate,
2-hydroxy-1,3-diacryloxypropane,
2,2-bis[4-(acryloxymethoxy)phenyl]propane,
2,2-bis[4-(acryloxypolyethoxy)- phenyl]propane, dicyclopentenyl
acrylate, tricyclodecanyl acrylate,
tris(acryloxyethyl)isocyanurate, .epsilon.-caprolactone-modified
tris(acryloxyethyl)isocyanurate, tris(acryloxyethyl)isocyanurate,
and so on.
[0037] The maleimide compounds are those having at least two
maleimide groups in their molecule, and examples thereof include
1-methyl-2,4-bismaleimide benzene, N,N'-m-phenylenebismaleimide,
N,N'-p-phenylenebismaleimide, N,N'-m-toluylenebismaleimide,
N,N'-4,4-biphenylenebismaleimide,
N,N'-4,4-(3,3'-dimethyl-biphenylene)bis- maleimide,
N,N'-4,4-(3,3'-dimethyldiphenylmethane)bismaleimide,
N,N'-4,4-(3,3'-diethyldiphenylmethane)bismaleimide,
N,N'-4,4-diphenylmethanebismaleimide,
N,N'-4,4-diphenylpropanebismaleimid- e, N,N'-4,4-diphenyl ether
bismaleimide, N,N'-3,3'-diphenyl sulfone bismaleimide,
2,2-bis[4-(4-maleimidophenoxy)phenyl]propane,
2,2-bis[3-s-butyl-4,8(4-maleimidophenoxy)phenyl]propane,
1,1-bis[4-(4-maleimidophenoxy)phenyl]decane,
4,4'-cyclohexylidene-bis[1-(- 4-maleimidophenoxy)-2-cyclo
hexyl)benzene, 2,2-bis[4-(4-maleimidophenoxy)p-
henyl]hexafluoropropane, and so on. These may be used alone or in
combination and may be used together with an allyl compound, such
as allylphenol, allylphenyl ether, or allyl benzoate
[0038] In the present invention, the radically polymerizable
substances as described above may be used alone or in combination,
and the adhesive film of the present invention preferably contains
at least a radically polymerizable substance having the viscosity
at 25.degree. C. in the range of 100,000-1,000,000 mPa.s and
particularly preferably contains a radically polymerizable
substance having the viscosity (25.degree. C.) of 100,000-500,000
mPa.s. The viscosity of the radically polymerizable substance can
be measured with a commercially available E-type viscometer. If the
viscosity at 25.degree. C. is less than 100,000 mPa.s, the
adhension becomes too high, or a part of the adhesive film
protrudes when it is formed in a tape-like form when compared with
the case where the viscosity is not less than 100,000 mPa.s. If the
viscosity at 25.degree. C. exceeds 1,000,000 mPa.s, the adhesive
film looses flexibility, thereby making a slit process difficult,
when compared with the case where the viscosity is not more than
1,000,000 mPa.s.
[0039] Among the radically polymerizable substances urethane
acrylate or urethane methacrylate is preferably applicable in terms
of adhesion and it is particularly preferable to use them in
combination with a radically polymerizable substance exhibiting Tg
of not less than 100.degree. C. singly after crosslinked with an
organic peroxide used for improvement in heat resistance.
[0040] The radically polymerizable substance used in the present
invention can be one having a dicyclopentenyl group and/or a
tricyclodecanyl group and/or a triazine ring. It is particularly
preferable to use a radically polymerizable substance having a
tricyclodecanyl group, because heat resistance improves more
sufficiently. Furthermore, the radically polymerizable substance
having a tricyclodecanyl group is preferably an acrylate or a
methacrylate. The adhesive film for circuit connection according to
the present invention may optionally contain a polymerization
inhibitor such as hydroquinone or hydroquinone methyl ethers as
occasion may demand.
[0041] The radically polymerizable substance used in the present
invention preferably has a triazine ring.
[0042] Furthermore, the radically polymerizable substance having
the phosphate structure is preferably used in the amount of 0.1-10
parts by weight, relative to 100 parts by weight of the sum of
film-forming polymer and radically polymerizable substance, and
more preferably in the amount of 0.5-5 parts by weight. In this
case, bond strength is improved on inorganic surfaces such as
metal. The radically polymerizable substance having the phosphate
structure is obtained as a reaction product of anhydrous phosphoric
acid and 2-hydroxyl (meth)acrylate. Specific examples of the
radically polymerizable substance having the phosphate structure
include 2-methacryloyloxy ethyl acid phosphate, 2-acryloyloxy ethyl
acid phosphate, and so on. These may be used alone or in
combination.
[0043] The film-forming polymer used in the present invention can
be selected from polystyrene, polyethylene, polyvinyl butyral,
polyvinyl formal, polyimide, polyamide, polyester, polyvinyl
chloride, polyphenylene oxide, urea resin, melamine resin, phenol
resin, xylene resin, epoxy resin, polyisocyanate resin, phenoxy
resin, polyimide resin, and so on, among which a resin having a
functional group such as hydroxyl is more preferably applicable in
order to improve adhesion. It is also possible to use these
polymers modified with a radically polymerizable functional group.
A molecular weight of these polymers is preferably
10,000-1,000,000. If the molecular weight is less than 10,000, a
film-forming ability becomes lower; if the molecular weight exceeds
1,000,000, the mixing property will degrade.
[0044] The film-forming polymer is preferably included in the
amount of 80-180 parts by weight relative to 100 parts by weight of
the radically substance. If the amount of the film-polymerizable
forming polymer is less than 80 parts by weight, the film-forming
ability becomes lower, when compared with the case where the amount
of the film-forming polymer is not less than 80 parts by weight. If
the amount of the film-forming polymer exceeds 180 parts by weight,
the film-forming polymer becomes more difficult to mix with the
radically polymerizable substance and the like, when compared with
the case where the amount of the film-forming polymer is not more
than 180 parts by weight.
[0045] Furthermore, the circuit-connection adhesive film of the
present invention may also contain a filler, a softener, a
promoter, an antioxidant, a coloring agent, a flame retardant, a
thixotropic agent, and/or a coupling agent, and contain phenol
resin, melamine resin, isocyanates, and so on.
[0046] The circuit-connection adhesive film of the present
invention preferably contains a filler, because it improves
connection reliability or the like. The filler can be used if the
maximum size thereof is less than the particle sizes of the
conductive particles, and is preferably contained in the range of
5-60% by volume. If the amount of the filler is less than 5% by
volume, the reliability of the electrical continuity becomes lower,
when compared with the case where the amount is not less than 5% by
volume. If the amount exceeds 60% by volume, the effect of
improvement in reliability will saturate, when compared with the
case where the amount is not more than 60% by volume. The coupling
agent is preferably an agent containing any of a vinyl group, an
acrylic group, an amino group, an epoxy group, and an isocyanate
group, in terms of improvement in adhesion.
[0047] The circuit-connection adhesive film of the present
invention preferably further contains electrically conductive
particles. In this case, where the circuit-connection adhesive film
is used for connection between circuit members, the connection
reliability between circuit electrodes can be more improved, in
comparison with the case where the circuit-connection adhesive film
without conductive particles is used. The conductive particles can
be selected from metal particles of Au, Ag, Ni, Cu, solder, or the
like, carbon particles, and so on, and, in order to obtain a
satisfactory pot life, the surface layer of the particles is
preferably Au, Ag, or a noble metal element of the platinum group
and more preferably Au, instead of the transition metals such as Ni
and Cu. The conductive particles may also be those obtained by
coating the surface of the transition metals such as Ni with one of
the noble metals such as Au. The conductive particles may be
preferably plastic-core particles obtained by forming the
aforementioned conductive layer on a non-conductive material of
glass, ceramics, plastics, or the like by coating or the like and
forming the outermost layer of a noble metal thereon, or thermally
melting metal particles, because they are deformable with
application of heat and pressure so as to increase the contact area
with electrodes during connection, thereby improving reliability.
The thickness of the coating layer of the noble metal is preferably
not less than 100 .ANG., in order to achieve good resistance.
However, in cases where the layer of the noble metal is provided on
the transition metal such as Ni, the thickness of the coating layer
is preferably not less than 300 .ANG., because free radicals are
produced by redox action induced by deficiency of the noble metal
layer, deficiency of the noble metal layer occurring during mixing
and dispersing of the conductive particles, or the like, so as to
cause reduction of the pot life. The conductive particles are to be
properly used according to applications, within the range of 0.1 to
30% by volume relative to 100% by volume of the adhesive component.
The amount of the conductive particles is more preferably within
the range of 0.1-10% by volume in order to prevent a short circuit
between adjoining circuits or the like due to excess conductive
particles
[0048] If the circuit-connection adhesive film of this
configuration is formed of two or more separate layers, including a
layer containing the curing agent to generate free radicals and a
layer containing the conductive particles, an improvement in the
pot life is achieved in addition to the conventional effect of
enabling increase of pattern density.
[0049] Next, an embodiment of the circuit connection structure of
the present invention will be described with reference to FIG.
1.
[0050] FIG. 1 is a sectional view showing the preferred embodiment
of the circuit connection structure of the present invention As
shown in FIG. 1, the circuit connection structure 100 of the
present embodiment has a first circuit member 20, a second circuit
member 30, and a circuit connection member 10 disposed between the
first circuit member 20 and the second circuit member 30. The first
circuit member 20 has a first circuit substrate 21, and first
circuit electrodes 22 provided on one surface 21a of the first
circuit substrate 21. The second circuit member 30 has a second
circuit substrate 31, and second circuit electrodes 32 provided on
one surface 31a of the second circuit substrate 31. On the other
hand, the circuit connection member 10 connects the first circuit
member 20 to the second circuit member 30 and contains a cured
material 11. Here the circuit connection member 10 is obtained by
performing a curing process of heating and pressing the
circuit-connection adhesive film. Namely, the circuit connection
member 10 is a cured product of the circuit-connection adhesive
film. The circuit connection member 10 may contain electrically
conductive particles 7.
[0051] The circuit connection structure 100 of the present
embodiment is obtained by a production method described below.
[0052] Specifically, as shown in (a) in FIG. 2, the first step is
to prepare the first circuit member 20 with the first circuit
electrodes 22 and the second circuit member 30 with the second
circuit electrodes 32. In this step, for example, the first circuit
member 20 is a flexible substrate. The second circuit member 30 is
not shown in (a), but is shown in (c).
[0053] Then the circuit-connection adhesive film 40 is transferred
onto the first circuit member 20 to be temporarily fixed. The
circuit-connection adhesive film 40 is comprised of the
aforementioned circuit-connection adhesive film. In the present
embodiment, the circuit-connection adhesive film 40 is composed,
for example, of one layer, and contains the aforementioned curing
agent, the aforementioned radically polymerizable substance, the
aforementioned film-forming polymer, and the conductive particles
7. In this step, the circuit-connection adhesive film 40 is drawn
out from a state in which it is wound around a reel.
[0054] Then the first circuit member 20 in the state in which the
circuit-connection adhesive film 40 is temporarily fixed thereon
(cf. (b) in FIG. 2) is transported to a place for connection
between the first circuit member 20 and the second circuit member
30.
[0055] Then, as shown in (c) in FIG. 2, the first circuit member 20
and the second circuit member 30 are placed in a state in which the
first circuit electrodes 22 and the second circuit electrodes 32
face each other, and the aforementioned circuit-connection adhesive
film 40 is interposed between the first circuit electrodes 22 and
the second circuit electrodes 32 placed in the facing state.
Subsequently, the circuit-connection adhesive film 40 is heated and
pressed to effect the curing process. In this manner the circuit
connection member 10 is formed between the first and second circuit
members 20, 30. The curing process can be performed by an ordinary
method and the method is properly selected depending upon the
adhesive composition. In this manner the first circuit electrodes
22 and the second circuit electrodes 32 are electrically
connected.
[0056] In the circuit connection structure 100 obtained by the
above production method, the adhesive film 40 has excellent
connection processability with the first circuit member 20 of the
flexible substrate. Specifically, an improvement is made in
transferability onto the first circuit member 20 of the flexible
substrate. In addition, the flexible substrate becomes unlikely to
drop with vibration during the transportation to the next process.
Furthermore, after the process of transferring the
circuit-connection adhesive film 10 onto the first circuit member
20 of the flexible board, the circuit-connection adhesive film 10
becomes unlikely to peel off the base film. Yet furthermore, even
if the circuit-connection adhesive film 10 several ten meters or
more long is wound around a reel and kept still at room temperature
for a long time, the back transfer of the circuit-connection
adhesive film 10 onto the base film is fully prevented, so as to
well overcome the problem of failure in drawing the desired
circuit-connection adhesive film out of the reel. This makes it
feasible to improve productivity and to achieve reduction of cost
for the circuit connection structure 100.
[0057] In the above production method of the circuit connection
structure 100, the first circuit member 20 is the flexible
substrate, but the second circuit member 30 may be formed as a
flexible substrate instead of the first circuit member 20, or the
first circuit member 20 and the second circuit member 30 both may
be formed as flexible substrates.
[0058] In the above embodiment, the circuit-connection adhesive
film 40 is comprised of one layer and the one layer contains the
curing agent, the radically polymerizable substance, the
film-forming polymer, and the conductive particles 7; however, the
circuit-connection adhesive film of the present invention may be
comprised of a first layer 50 containing the conductive particles
7, and a second layer 60 containing the curing agent to generate
free radicals, as shown in FIG. 3. In this case, it becomes
feasible to achieve increase of pattern density and improvement in
the pot life. The circuit-connection adhesive film may be comprised
of two or more layers.
EXAMPLES
[0059] The present invention will be described below in more detail
on the basis of examples.
Example 1
[0060] Mixed into 130 parts by weight of a solution containing 40%
by weight of a phenoxy resin (weight-average molecular weight:
45,000) dissolved in a 50:50 mixed solvent of toluene and ethyl
acetate were 10 parts by weight of urethane acrylate having the
viscosity at 25.degree. C. of 250,000 mPa.s, 25 parts by weight of
bis(acryloxyethyl) isocyanurate having the viscosity at 25.degree.
C. of 8,000 mPa.s, 10 parts by weight of dimethylol tricyclodecane
diacrylate having the viscosity at 25.degree. C. of 150 mPa.s, and
3 parts by weight of 2-methacryloyloxy ethyl acid phosphate as the
radically polymerizable substance, and 4 parts by weight of a
hydrocarbon-diluted solution containing 50% by weight of
2,5-dimethyl-2,5-bis(2-ethylhexanoylperoxy)he- xane as a free
radical generator. Thereafter, this mixture was uniformly stirred.
Furthermore, mixed and dispersed in this mixture was 3% by volume
of conductive particles with the average particle size of 5 .mu.m
formed by providing surfaces of polystyrene-core particles with a
nickel layer 0.2 .mu.m thick and forming a gold layer 0.04 .mu.m
thick over the outside of the nickel layer. The coating solution
obtained in this manner was applied onto a PET film with a
surface-treated side 80 .mu.m thick by a coater and dried with hot
air at 70.degree. C. for ten minutes. Obtained in this manner was
the circuit-connection adhesive film (in the width of 15 cm and the
length of 60 m) having the adhesive layer in the thickness of 20
.mu.m. The resultant adhesive film was cut into the width of 1.5 mm
and wound by 50 m around a side face (1.5 mm thick) of a plastic
reel with the inside diameter of 40 mm and the outside diameter of
48 mm while keeping the adhesive film surface inside, to obtain the
circuit-connection adhesive film of tape shape. The temporary
fixing power of the obtained circuit-connection adhesive film to
the flexible substrate was 110 N/m. The temporary fixing power of
the circuit-connection adhesive film to the flexible substrate was
measured by the method as described previously.
Connection of Circuits
[0061] The circuit-connection adhesive film of tape shape prepared
in Example 1 was kept still at room temperature for three days, and
thereafter the desired adhesive film was able to be drawn out of
the reel, without back transfer of the adhesive film layer onto the
base film.
[0062] Then the adhesive surface of the circuit-connection adhesive
film (in the width of 1.5 mm and the length of 3 cm) was
transferred onto an ITO-coated glass substrate by heat and pressure
under the conditions of 70.degree. C. and 1 MPa for three seconds,
and the PET film was peeled off. The number of samples prepared was
20, and all the circuit-connection adhesive films (width 1.5 mm and
length 3 cm) were successfully transferred onto the ITO-coated
glass substrate. Then a flexible printed circuit board (FPC) having
six hundred tinned copper circuits in the pitch of 50 .mu.m and in
the thickness of 18 .mu.m was pressed onto the circuit-connection
film under the conditions of 24.degree. C. and 0.5 MPa for five
seconds to be temporarily fixed. All the temporarily fixed FPCs
(the number of samples: 20) did not drop even with vertical and
lateral vibration together with the glass substrate and had no
problem in transportation for placement onto a main bonder being
the next process. Then the glass substrate on which the FPC was
temporarily fixed by the circuit-connection film was set on the
main bonder and was heated and pressed under the conditions of
160.degree. C. and 3 MPa for ten seconds by a heat tool from the
flexible circuit board side to effect connection in the width of 2
mm.
Measurement of Connection Resistance
[0063] After the connection of circuits, the resistance between
adjoining circuits of the FPC including the above connection part
was measured with a multimeter at the beginning and at the time
after held in a high-temperature high-humidity chamber of
85.degree. C. and 85% RH for 1000 hours. The resistance was defined
as an average of resistances measured at 50 points between
adjoining circuits.
[0064] The initial connection resistance of the circuit connection
structure using the circuit-connection adhesive film obtained in
Example 1 was 1.5 .OMEGA. in average, and the resistance after the
1000 h high-temperature high-humidity (85.degree. C. and 85% RH)
test was 2.5 .OMEGA. in average. Therefore, there was little change
in the connection resistance, so as to ensure high connection
reliability.
Measurement of Bond Strength
[0065] After the connection of circuits, the bond strength was
measured by 90-degree peeling at the peel speed of 50 mm/min. The
circuit connection structure in Example 1 demonstrated the good
bond strength of about 1000 gf/cm.
Comparative Example 1
[0066] A circuit-connection adhesive film with an adhesive layer 20
.mu.m thick was prepared in the same manner as in Example 1 except
that 45 parts by weight of bis(acryloxyethyl) isocryranurate having
the viscosity at 25.degree. C. of 8,000 mPa.s and 3 parts by weight
of 2-methacryloyloxy ethyl acid phosphate were used as the
radically polymerizable substance. The temporary fixing power of
the circuit-connection adhesive film obtained was 20 N/m.
Connection of Circuits
[0067] The circuit-connection adhesive film of tape shape prepared
in Comparative Example 1 was kept still at room temperature for
three days and even thereafter, the desired adhesive film was
successfully drawn out of the reel, without back transfer of the
adhesive film layer onto the base film.
[0068] Then the adhesive surface of the circuit-connection adhesive
film (width 1.5 mm and length 3 cm) of tape shape was transferred
onto an ITO-coated glass substrate by heating and pressing under
the conditions of 70.degree. C. and 1 MPa for three seconds, and
the peeling test of the PET film was conducted. However, eight
samples out of twenty samples failed to transfer the
circuit-connection adhesive film onto the ITO-coated glass
substrate. Then, using twelve samples which achieved successful
transfer of the circuit-connection adhesive film onto the
ITO-coated glass substrate, a flexible printed circuit board (FPC)
having six hundred tinned copper circuits in the pitch of 50 .mu.m
and in the thickness of 18 .mu.m was pressed onto the
circuit-connection adhesive film under the conditions of 24.degree.
C. and 0.5 MPa for five seconds to be temporarily fixed. Then the
glass substrates (twelve samples) in which the FPC was temporarily
fixed by the circuit-connection adhesive film were moved to be set
on the main bonder, but seven FPCs peeled off the
circuit-connection adhesive film because of vibration during
transportation and were thus not brought to main bonding.
Comparative Example 2
[0069] A circuit-connection adhesive film with an adhesive layer 20
.mu.m thick was prepared in the same manner as in Example 1, except
that 45 parts by weight of dimethylol tricyclodecane diacrylate
having the viscosity at 25.degree. C. of 150 mPa.s, and 3 parts by
weight of 2-methacryloyloxy methacryloyloxy ethyl acid phosphate
were used as the radically polymerizable substance. The temporary
fixing power of the circuit-connection adhesive film obtained was
200 N/m.
Connection of Circuits
[0070] The circuit-connection adhesive film of tape shape prepared
in Comparative Example 2 had too strong tackiness, and had the
problem that after kept still at room temperature for three days,
the adhesive film layer was back-transferred onto the base film and
the desired adhesive film was not successfully drawn out of the
reel, resulting in failure in being fed to connection of
circuits.
Comparative Example 3
[0071] A circuit-connection adhesive film with an adhesive layer 20
m thick was prepared in the same manner as in Example 1, except
that 45 parts by weight of triethylene glycol diacrylate having the
viscosity at 25.degree. C. of 10 mPa.s and 3 parts by weight of
2-methacryloyloxy ethyl acid phosphate were used as the radically
polymerizable substance. The temporary fixing power of the
circuit-connection adhesive film obtained was 230 N/m.
Connection of Circuits
[0072] The circuit-connection adhesive film of tape shape prepared
in Comparative Example 3 had too strong tackiness and thus had the
problem that after kept still at room temperature for three days,
the adhesive film layer was back-transferred onto the base film and
the desired adhesive film was not successfully drawn out of the
reel, thus resulting in failure in being fed to connection of
circuits.
[0073] The results of above Example 1 and Comparative Examples 1-3
confirmed that the circuit-connection adhesive film of the present
invention has excellent connection processability with the flexible
substrate.
[0074] As described above, the circuit-connection adhesive film of
the present invention is able to implement both the satisfactory
transferability and temporary fixing power onto the flexible
substrate as a circuit member, which were not achieved by the
radical curing type circuit-connection adhesive films, and has the
excellent connection processability in connection between circuit
members.
[0075] Since the adhesive film has the excellent connection
processability with the flexible substrate, the circuit connection
structure of the present invention improves productivity and
enables reduction of cost.
* * * * *